4 : 5
Explanation:
Kate can mow at a constant rate of 4/5 lawns per hour.
So, we can represent this in the following manner:
Kate can mow 4 lawns in an interval of 5 hours at a constant rate.
We are asked to determine the ratio of lawns per hour.
Therefore, the ratio of lawns per hour is 4 : 5. ( Answer )